Review: The New IWC Portugieser Eternal Calendar

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Speak of IWC and the first thing that comes to mind is ‘pilot’s watches’. The second thing, however, would inevitably be the cruciform layout of the brand’s perpetual calendar displays. Developed by now-retired Kurt Klaus during the early 1980s, IWC’s perpetual calendar mechanism made its debut in the Da Vinci Perpetual Calendar in 1985. The ingenious mechanism developed under the code name “Operation Eternity” took the brand into the realms of haute horlogerie and is regarded as a significant milestone in watchmaking even today. Over the years, IWC have continuously improved upon the original mechanism, coming up with innovative timepieces such as the Perpetual Calendar Digital Date-Month along the way with digital displays, and the Portugieser Perpetual Calendar with double-moon display for the northern and southern hemispheres.

IWC Portugieser Eternal Calendar

This year, IWC takes a major leap in the history of its most iconic complication. The Schaffhausen-based watchmaker has developed a new perpetual calendar movement that is juiced to the gills, truly putting the “perpetual” into the “calendar”. This super perpetual calendar is known as a secular calendar which will require no adjustments for a least the next thousand years. Oh, and the movement also comes with a moon phase indicator of unprecedented accuracy as a bonus. Here, we bring you the details and our honest thoughts on the new and aptly named IWC Portugieser Eternal Calendar.

The Case, Dial, and Hands

The case of the Portugieser Eternal Calendar measures 44.4 mm x 15 mm. It sounds huge – and it is – but also impressive at the same time, because it is only negligibly larger (by 0.2 mm x 0.1 mm) than the standard issue Portugieser Perpetual Calendar despite significantly enhanced movement functionality. The case is rendered in platinum, which feels like the right choice for the brand’s first and currently only secular calendar wristwatch. The best part about the case, though, has to be the front-and-back box sapphire crystals that give the Portugieser Eternal Calendar a neo-vintage vibe, reminiscent of old savonette pocket watches. The finissage on the case is unchanged relative to that of the Portugieser Perpetual Calendar – perhaps a missed opportunity to add more hand-finished nuance, as it’s always been fairly austere.

Size notwithstanding, the casing of the Eternal Calendar sees only one design change relative to the Perpetual Calendar: the introduction of box crystals for the front and back of the case.

The most drastic change in appearance comes from the dial. The use of glass, frosted and lacquered white on the underside, as the material of choice for the main dial is refreshing. IWC takes it further by applying separate glass sub-dials to serve as the displays of the secular calendar. On one hand, this novel aesthetic hurts legibility and looks sterile. On the other, the layers upon layers of superposed glass imparts to the watch an air of ethereal beauty. The sub-dial at the 12 o’clock position houses the perpetual moon phase display for both northern and southern hemispheres, along with the age of the moon indicator. The sub-dial at 3 o’clock displays the date and power reserve radially. Moving on to the 6 o’clock sub-dial, there’s the month display as well as the IWC SHAFFHAUSEN printed script. And last but not least, at 9 o’clock, there’s the running seconds, and the day display that’s just outboard of the seconds track. These glass sub-dials add depth to the dial and give the printed displays a floating effect. Adding further depth and three dimensionality is a white lacquered flange printed with chemin de fer minute track that sits between the dial and the box crystal. Meanwhile, the calendar year is indicated digitally through an aperture between 7 and 8 o’clock. Another aperture (this time, round) between 4 and 5 o’clock reveals the key module that brings the secular calendar to reality.

Ice cold: Transparency and ether are the themes here as IWC goes heavy on glass with the Portugieser Eternal Calendar.

Relative to the acreage of the dial, the many hands on the Portugieser Eternal Calendar are very thin, which contributes to the legibility criticism that has been raised. These hands – along with the applied hour markers – are also rhodium-plated, meaning there’s not a whole lot of contrast between them and the dial. Combined with the fact that the prints and appliques cast shadows on the lacquered underside of the dial and you get a perfect storm for suboptimal readability. On the plus side, while the lancet hands of the calendar displays are really fine, they are heat-blued, which helps in separating the calendar functions from the others.

The Movement

Driving the Portugieser Eternal Calendar is the 54-jewel, in-house developed and manufactured Calibre 52640. The highlight of the automatic movement is its super-accurate perpetual calendar, known as the secular calendar. The secular calendar watch may not be a new invention, but the number of examples that existed prior to this year could literally be counted on one hand. But just how is the secular calendar more accurate than the perpetual calendar? It’s all got to do with the lesser known rules of the leap year. Common knowledge dictates that any year divisible by four is a leap year (this year is a leap year, for instance). But it gets more complicated. Years divisible by 100, like the year 2100, are not leap years even though they are divisible by four – this is also where the conventional perpetual calendar fails. However, if a year is divisible by 400, such as the year 2000 or 2400, it is considered a leap year. All these corrections are necessary to account for the fact that the true length of a year (the sidereal year) is in fact 365.2425 days and not the 365 days we experience on most years.

The Calibre 52640 as seen through the sapphire crystal case back.

In order to correct for these rule exceptions, IWC have introduced a seemingly simple solution: the integration of a 400-year wheel to Kurt Klaus’ perpetual calendar module. The wheel completes just one revolution every four centuries and makes sure that the calendar skips three leap years over that period, the first of which are years 2100, 2200, and 2300. As a result, the Eternal Calendar thusly remains accurate until at least year 3999, given that there isn’t yet a consensus on whether year 4000 should be a leap year (it doesn’t look like it’s going to be one, which makes it another likely exception to the rules).

But wait, there’s more. The moon phase indicator in the Calibre 52640 approximates eternity even more closely than the secular calendar function; it deviates from the moon’s actual orbit by one day after a whopping 45 million years – a new world record. This was made possible thanks to newly developed gearing between the barrel and the moon disc. Considering that the moon phase indicator of a contemporary fine timepiece is typically accurate to within an-already-impressive one day every 122 years, this makes the Portugieser Eternal Calendar all the more incredulous. It leaves the previous record holder (the Lune Perp├ętuelle by Andreas Strehler) in the dust by more than an order of magnitude of accuracy.

The sizeable Calibre 52640 has a power reserve of 7 days and operates at a modern 4 Hz frequency. Finissage on the movement is attractive and neat despite the lack of hand-finishing. The usual decorative techniques can be seen applied to components through the sapphire crystal case back: perlage on the main plate, circular Geneva waves on the bridges, circular brushing on the wheels, beveling on edges, bluing of screws, and mirror polishing on screw heads, among other things.

The Competitive Landscape

The Portugieser Eternal Calendar is about to make the secular calendar much less niche – good news (or is it bad news?) for fans of super-accurate perpetual calendar watches. Before IWC crashed the party, the secular calendar complication was only found in fewer than half a dozen watch references that were either extremely expensive or absurdly rare, or both. Think Patek Philippe Calibre 89 or the Franck Muller Aeternitas Mega 4. The Portugieser Eternal Calendar is not a limited edition timepiece. Its price tag is the only limiting factor, clocking in at CHF150,000. At first glance, the price would seem high for a watch whose finishing is more industrial than artisanal. But it’s important to note that integrating the secular calendar module and changing the gearing for the moon phase are no simple tasks. There’s also economics at play: the Portugieser Eternal Calendar is the first truly ‘accessible’ wristwatch with a secular calendar complication and a bonus moon phase indicator of record-breaking accuracy. There is really no competition around (yet) to warrant an aggressive pricing strategy – and that’s perfectly fine.

No surprises that the Portugieser Eternal Calendar sits huge on the wrist. This isn’t a watch that should (or can) be hidden under a sleeve, though.

If IWC’s new secular calendar watch is out of your budget, look no further than the brand’s already established perpetual calendar watches. There are reasons why the perpetual calendar is an IWC signature – ease of use, and reliability, to name two. The brand’s latest expression of the perpetual calendar is all the more reason to join in on the fun: the Big Pilot’s Watch Perpetual Calendar Top Gun Lake Tahoe. Introduced in 2023, this is IWC’s first perpetual calendar watch in ceramic. It being part of the Top Gun collection will only make it even more popular, in addition to its genuinely stunning aesthetics. Priced at USD40,900 (on its debut), it is over three times less expensive and is a perfectly valid alternative to the record-breaker.

The IWC Big Pilot’s Watch Perpetual Calendar Top Gun Lake Tahoe

And speaking of perfectly valid alternatives, there’s also the Andreas Strehler Lune Exacte, not to be confused with the Lune Perp├ętuelle that came first in 2014 to set the previous moon phase record. The Lune Exacte is just like its predecessor but with one really cool upgrade: the ability to set and read the moon phase indicator to unparalleled precision. It comes with a Vernier scale which aids in the reading and setting of the age of the moon to an astonishing 3 hours at any time. So, on top of being accurate up to one day every 2 million years, the Lune Exacte also displays the age of the moon precisely in days and further increments of 3 hours. As if that’s not enough, the watch is fitted with a remontoir and features finissage worth of haute horlogerie. Priced at CHF125,000, this is one for the connoisseurs and movement geeks (with deep pockets).

The Andreas Strehler Lune Exacte

Final Thoughts

IWC breaks the market once again with smart watchmaking and not charging a million dollars. Sarcasm aside, the Portugieser Eternal Calendar is indeed a revelation. It has a legitimate secular calendar and – by far – the most accurate moon phase indicator ever made, all thanks to clever watchmaking. The watch isn’t cheap by any means, but when compared to like-alternatives in the market, you’ll just be glad you can now buy one in a regular boutique. The cost is kept relatively low compared to other existing secular calendar watches by means of efficient manufacturing and machine finishing. Nevertheless, the Eternal Calendar still boasts mind-blowing specs. The over-engineering of mechanisms is often twisted as a flex in horology, but the reality is it just leads to longevity issues and maintenance grievances. The fact that the solution that IWC found was relatively simple mechanistically gives them the ultimate bragging rights. Expect more variations of the model to arise in the future.


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